The disclosed embodiments generally relate to self-releasing fuser members useful in electrostatographic apparatuses. In embodiments, the fuser member can reduce or dispense with the need for fuser release agents (such as fuser oils) in electrostatographic apparatuses.
In an electrostatographic printing apparatus, a light image of an original to be copied is recorded in the form of an electrostatic latent image upon a photosensitive member and the latent image is subsequently rendered visible by the application of electroscopic thermoplastic resin particles, which are commonly referred to as toner. The visible toner image is then in a loose powdered form and can be easily disturbed or destroyed. The toner image is usually fixed or fused upon a support which can be a photosensitive member itself or other support such as plain paper.
The use of thermal energy for fixing toner images onto a support member is known in the art. In order to fuse electroscopic toner material onto a support surface permanently by heat, it is necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become tacky. This heating causes the toner to flow to some extent into the fibers or pores of a support (such as a page of paper). Thereafter, as the toner material cools, solidification of the toner material causes the toner material to be firmly bonded to the support.
Thermoplastic resin particles can be fused to a support by heating to a temperature of between about 90° C. and about 160° C. or higher depending upon the softening range of the particular resin used in a toner. It is not desirable, however, to raise the temperature of the support substantially higher than about 200° C., because of the tendency of certain substrates to discolor at such elevated temperatures, particularly when the support is paper.
Several approaches to thermal fusing of electroscopic toner images have been described in the prior art. These methods include providing the application of heat and pressure substantially concurrently by various means: a roll pair maintained in pressure contact; a belt member in pressure contact with a roll; and the like. Heat can be applied by heating one or both of the rolls, plate members or belt members. The fusing of the toner particles takes place when the proper combination of heat, pressure and contact time is provided. The balancing of these parameters to bring about the fusing of the toner particles is well known in the art, and the parameters can be adjusted to suit particular machines or process conditions.
Fuser roll topcoat materials are often made from low surface energy fluoropolymers such as perfluoroalkoxy, or other TEFLON®-like fluoropolymers, or fluoroelastomers such as those having the trademark VITON® from DuPont, which are expected to provide heat- and wear-resistance, conformability, and improved release at the fusing nip. VITON® GF, a fluoroelastomer, shows good mechanical properties but poor toner release. A current issue with existing fuser materials (such as VITON® materials) is the requirement for a release agent, e.g., PDMS (polydimethylsiloxane)-based fuser oil, for release of toner and other contaminants. The use of fuser oil increases the cost of the fuser release system and causes end-use problems because the silicone oil often remains on the prints. The fuser oil can result in difficulties in end uses of printed materials such as binding, lamination, or other processes requiring surface adhesion. New topcoat materials are required for low-oil or oil-less (machines that do not require a release agent or fuser oil), long-lifetime, high performance fusing applications.
During operation of a fusing system in which heat is applied to cause thermal fusing of the toner particles onto a support, both the toner image and the support are passed through a nip formed between the roll pair or plate or belt members. The concurrent transfer of heat and the application of pressure in the nip affect the fusing of the toner image onto the support. It is important in the fusing process that no offset of the toner particles from the support to the fuser member take place during normal operations. Toner particles that offset onto the fuser member can subsequently be transferred to other parts of the machine or onto the support in subsequent copying cycles, thus increasing the background or interfering with the material being copied. A “hot offset” occurs when the temperature of the toner is increased to a point where the toner particles liquefy and a splitting of the molten toner takes place during the fusing operation with a portion remaining on the fuser member. The hot offset temperature or degradation to the hot offset temperature is a measure of the release property of a fuser roll, and accordingly it is desired to provide a fusing surface, which has a low surfaced energy to provide the necessary release. To ensure and maintain good release properties of the fuser roll, release agents can be applied to the fuser roll during the fusing operation. These materials are often applied as thin films of, for example, silicone oils to prevent toner offset.
While highly successful in providing a fusing surface with a very low surface energy to provide excellent release properties to ensure that the toner is completely released from the fuser roll during the fusing operation, these release agent systems suffer from a significant deterioration in physical properties over time in a fusing environment. In particular, the silicone oil release agents tend to penetrate the surface of silicone elastomer fuser members resulting in swelling of the body of the elastomer causing major mechanical failure including debonding of the elastomer from the substrate, softening and reduced toughness of the elastomer causing it to crumble, contaminating the machine and providing non-uniform delivery of release agent.
The disclosure contained herein describes embodiments to address one or more of the problems described above.